1. Technical Field
The invention relates generally to integrated circuits, and more specifically, to automatic power reduction for integrated circuits.
2. Background Art
In many battery-powered systems, such as portable electrical equipment, achieving low-power consumption with minimal battery drain current is important. To achieve low-power consumption, many portable systems have a "sleep mode" or standby mode that generally decreases the clock frequency. Then, when an input stimulus is detected, the clock frequency is brought back up to full-speed for active mode. Similarly, when the system is in active mode, a reduced clock speed may be used for power savings depending on the level of activity of the system or parts of the system. Two examples of this type of power reduction is found in the following U.S. Patents: U.S. Pat. No. 5,617,572, issued in April 1997 to Pearce et al.; and U.S. Pat. No. 5,475,847, issued in December 1995 to Ikeda et al. Pearce describes various I/O devices that are powered down individually through timers. When the allotted time of an I/O device has elapsed and the I/O device has not experienced any activity, the powering level of that I/O device is decremented into a deeper sleep mode. Ikeda teaches a computer system that operates at a full clock speed and at a reduced clock speed for power savings. The activity level of the system will determine the appropriate clock speed.
Although power savings is addressed in the aforementioned patents, the reduction of power is dependant upon the activity level of the system. Other conditions, such as integrated circuit (IC) manufacturing tolerances, aging, temperature, and current usage that may affect the performance level of the system, and thus the power consumption, are not considered. Furthermore, many portable equipment applications require a state of "instant readiness" from which the equipment can immediately respond with full performance to an input stimulus. The conditions for maintaining "instant readiness" and minimal drain current for either active or standby modes are themselves in direct opposition.